At least one embodiment refers to a method for securely exchanging messages between at least two devices, each of them storing a shared secret key. The method comprises: at each device: generating a random number, then sending it to the other devices; determining a first key by a first operation based onto said secret key and each random number; determining a second key based on said first key and said random numbers; at a sending device: determining a pseudo message on the basis of the message and said random numbers; calculating then sending a cryptogram on the basis of said pseudo message and said second key; and at the receiving device: decrypting said cryptogram by means of said second key; and retrieving said message from said pseudo message.